Neutralization of the natural capacitive coupling of adjacent circuits



Apnl 7, 1931. Y J. FINCH 1,799,631

NEUTRALIZATION OF THE NATURAL CAPACITIVE COUPLING OF ADJACENT CIRCUITS Filed Sept. a, 1927 INVENTQR JAMES L. FINCH.

AVI'ORNEY Patented Apr. 7, 1931 H UNITED STATES PATENT OFFICE-f JAxEs L. FINCH, or cnANEoEn, NEW .iEnsEY, ASSIGNOR To EAnIo CORPORATION or AMERICA, A coEronA'rIoN OF DELAWARE nu'rnAmzA'rIoN on THE NATURAL CAPACITIVE COUPLING E ADJACENT cmcur'rs Application filed September 8, 1927. Serial No. 218,127.

This invention relates to neutralizing the natural capacitive coupling of adjacent circuits, and more particularly the antennae circuits of a multiplex transmission station.

Various methods have been proposed for so coupling a plurality of antennae circuits as to oppose the effect of their natural capacitive coupling. These known methods require the use of inductors which are sub'ected to a high potential, and'which' there ore present great difiiculties in insulation. It is an object of my invention to overcome this, which I do by locating a coupling inductor in the antennae circuits at such a point that 1 one of. the terminals of the inductor is at ground potential.

A further object of my invention isto greatly simplify and cheapen the equipment needed for neutralizing the antennae, and to 9 this end I have discovered that neutralization of the natural capacitive coupling may be accomplished by that natural inductive coupling is provided when the plurality of antennae are connected to a common'ground c.9125 connection.

In some cases a slmple'short ground connection may be insufficient for complete neutralization. With part of the natural capacitance neutralized, to neutralize the remainder by the usual type of inductance connected between the antennae to resonate with their natural capacitance is sometimes inconvenient, for the reduced capacitance requires increased inductance for resonance. Accordingly it is a further object of my invention to insure that the common ground connection provides suflicient coupling for complete neutralization, which vI do by inserting an inductor in the common ground connection.

is the multiple tuned antenna of F. W. Alexanderson. If several such antennae lie parallel to one another their mutual capacitive coupling is greatly increased. It is a more detailed object of my invention to provide for opposing the natural coupling of such antennae, and this I do in a simple manner by connecting one or more corresponding groundconnections of the antennae to com- =mon ground leads, and if necessary these An extensively used transmittingilantenna leads may include series coupling inductors. My invention is described more in detail in the following specification, which is accompanied by a drawing. in which Figure 1 represents my invention in-simplest form;

Figure 2 shows the use of an inductor in the common ground lead; and

Figure 3 represents the invention as applied to multiple tuned antennae.

In Figure 1 there are indicatedtransmitting antennae 2 and 4, energized by transmitters 6 and 8, and coupled together by the mutual capacitance of the antennae, represented by the condenser 10. I have found that if the antennae, instead of being separately grounded, are connected together through a common ground connection, such as that indicated at 12, the natural coupling provided by the commonlead 12in itself provides energy for opposing that transferred by the natural capacitance 10.

In some cases the coupling provided by a short direct ground connection may be insufficient tocompletely neutralize the effect of the capacitance 10. If it is inconvenient to extend the ground connection-the inductance thereof may be conveniently increased in the manner indicatedin Figure 2, in which a coupling inductor 14: is provided'in the common ground lead 12. If the transmitters 6 and'8 are high frequency alternators it is very desirable that one terminal of the alternators remain at ground potential, for otherwise the insulation may be broken down. The insertion of an inductor, such as 14:, tends to raise the potential at the grounded side of the alternators, which disadvantage may i be overcome by the insertion of condensers 16 and 18of proper magnitude to series resonate with the inductance 14,and thereby lower the potential-of the grounded alternator terminals to ground potential.

I am aware that it has already been proposed to neutralize antennae by the use of coupling inductors which are in series with the antennae, and such arrangements may superficially seem similar to the arrangement which I have indicated in Figure 2, but there are theseimportant diif erences; 'first,

that with my arrangement one terminal of the inductor is at ground potential, and the maximum potential applied to the inductor is that which is caused by the potential gradient across the inductor itself, which potential may be insulated without undue difiicu lty, whereas all prior arrangements have suggested the use of coupling inductors a situa d in the ntenna ci cuits ab the transmitters, and which therefore must be arranged for insulation against high po tentials, adding to their structural difficulty and expense; and second, that with my arrangement a simple ccnd-uctively connected inductor may be employed, whereas such prior arrangements as used series inductors had to use magnetic coupling, lest each alternator be short circuited to ground through the other alternator.

In Figure 3 I have indicated how my invention may be applied to closely located multiple tuned antennae. In that hgure the two antennas 20 and 22 are energized from transmitters 6 and 8, and are tuned by multiple ground connections such as 24 and 26. In

accordance with my invention one or more of these ground connections may be connected together and grounded through a common ground lead in order to provide coupling in opposition to the natural capacitive coupling of the antennae. In the particular case illustrated there are six antennae sections, and of the six tuning points alternate ones, such as 28 and 30, have been connected together and to ground through a common ground lead 32. As was before explained, this common ground lead may be increased in inductance by the insertion of a series inductor 34;. In this a there is no necess y to employ s i s o de ers, such as the conden rs 16 and 18 in Figure 2, for it is 1 .01 essential that the lower terminals of the tuning inductors he at ground potential. They are, of course, removed from ground potential only by the amount of the potential drop across the coupling inductor 3a.

' I he foregoing spec fic tion I ha e spoke of the coupling inductors as neutralizing the natural capacitive coupling of the antennae. It will be appreciated by those skilled in this art that such neutralization can only be made perfect at one frequency. Inasmuch as the multiplex channelstransmit at different frequencies it follows that there can be perfect neutralization only in one direction, the choice of which is optional. In practice it is customary to neutralize for a frequency intermediate the working frequencies, which is more satisfactory than might be predicted, because it is found in practice, and can be shown theoretically, that such neutralization causes that energy which is transferred from each antenna to the other of the antennae to be in proper phase relation to aid the total radiation. For these reasons I intend the claims which follow to include the cases where the neutralization is at any desired frequency, including the lower and higher transmission frequencies, as well as intermediate frequencies.

I claim:

1. In combination, two grounded circuits having natural capacitive coupling, and means for grounding the circuits and for coupling the circuits in opposition to their natural coupling comprising a common ground lead of suificient length that the in.- ductance of the common lead serves to appreciably oppose the natural capacitive coupling.

'2. A multiplex radiating system comprising a plurality of antennae, a plurality of transmitters, one coupled to each of said antennae, an inductor for coupling the antennae in opposition to their natural coupling, means connecting one end of said inductor directly to ground, and means connecting the other end of said inductor to the antennae.

'3. A multiplex radiating system comprising a plurality of antennae, a plurality of transmitters, one coupled to each of said antennze, and a common ground connection for the antennae of suflicient length that the in ductance of the common lead serves to appreciably oppose the natural capacitive coupling.

4:. A multiplex radiating system comprising a plurality of antennae, a plurality of transmitters, one coupled to each of said an tenure, a common ground connection for the antennae, and an inductor inserted in series in the common ground connection of sufficient inductance, together with the ground con nection, to neutralize the natural coupling between the antennae.

5. A multiplex radiating system comprising a plurality of multiple tuned antennae, a plurality of transmitters, one coupled to each of said antennae, and a plurality of common ground connections for the antennae of sufficient length that the inductance of the common lead serves to appreciably oppose the natural capacitive coupling of the antennae.

6. A multiplex radiating system comprising a plurality of multiple tuned antennae, a plurality of transmitters, one coupled to each of said antennae, a plurality of common ground connections for the antennae, and an inductor inserted in series in each of the common ground connections, said inductors having sufficient inductance together with the ground connection, to neutralize the natural coupling between the antennae.

7. In a system for transmitting or conveying intelligence from one geographically situated point to another geographically situated point by the utilization of propagated electromagnetic waves derived from the flow of high frequency undulatory electrical currents operated upon in accordance with the intelligence to be transmitted from the one geographically situated point to the other, the combination of two grounded circuits having natural capacitive coupling, and means grounding the two circuits and for coupling the circuits in opposition to their natural capacitive coupling comprising a connection having an inductive value to appreciably oppose the efiects produced by the natural capacitive coupling between the two grounded circuits of the system.

JAMES L. FINGH. 

